Crescimento, aspectos fisiológicos e metabolismo do nitrogênio em plantas de milho submetidas a deficiência hídrica e concentrações de brassinosteróides e Azospirillum.

Abstract

Abiotic stress, in particular the water deficit, reduces the productivity of vegetable crops, negatively impacting agricultural sustainability. To minimize these harmful effects on agriculture, several agronomic and physiological practices are being studied, such as the use of bacteria and water stress attenuators, such as Brassinosteroids, which are growth regulators. Considering the socioeconomic relevance of corn culture and its sensitivity when exposed to water deficit, the objective of the present study was to evaluate the action of Brassinosteroides and azospirillum on growth, physiological aspects and nitrogen metabolism during the vegetative phase of corn plants submitted to water deficiency. The experiment was carried out in a greenhouse, from December 2019 to January 2020, using corn plants, the hybrid K9606 VIP3. The experimental design used was completely randomized, in a 2x2x3 factorial scheme, with six replications, totaling 72 experimental units. The first factor corresponds to two water regimes (presence and absence of water deficiency). The second factor corresponds to seed inoculation (at the moment of sowing) of Azospirillum brasilense and absence of inoculation. And the third factor corresponds to the application of three concentrations of brassinosteroids (0, 0.3 and 0.6 μM Br). Before sowing, a part of the corn seeds were inoculated with azospirillum and another part was not. Brassinosteroids (0, 0.3 and 0.6 μM Br) were applied fifteen and thirty days after planting. Ten days after the last brassinosteroid application, stress was applied to the treatments that would receive the stress. Seven days after the application of water deficiency to corn plants, they were collected for biochemical analysis, being separated into leaf and root. Thus, evaluations related to plant growth and physiology were carried out. The absence of inoculation with Azospirillum brasilense and spraying of brassinosteroids at a concentration of 0.6 μM in corn plants under water stress conditions, showed increases in leaf number. Plants with water deficiency inoculated with bacteria and application of brassinosteroids in the highest concentration, mitigated the negative influences caused by stress, presenting an increase in the relative water content in corn plants. Plants with brassinosteroids in a concentration of 0.3 μM and inoculated, attenuated the effects of water stress, providing an increase in chlorophyll a. While, for chlorophyll b, only the presence of the hormone at a concentration of 0.3 μM promoted an increase in the values of this parameter. The interaction of brassinosteroids with the bacteria provided an increase in total soluble carbohydrates in the leaves and roots of corn plants subjected to water stress. Under water stress conditions, corn plants without inoculation and spraying 0.6 μM of brassinosteroids, promoted an increase in the starch content in the leaves. In the roots, only the presence of the bacteria without or with the application of 0.3 μM of brassinosteroids provided an increase in starch. The use of the plant growth promoting bacteria Azospirillum brasilense via seed and the application of brassinosteroids, alleviate the negative effects on nitrogen metabolism in leaves and roots caused by the occurrence of water deficiency in the corn crop.